Effects of addition of arginine, cystine, and glycine to the bovine milk-simulated amino acid mixture on the level of plasma and liver cholesterol in rats.

The effects of the addition of varying levels of arginine (Arg), cystine (Cys), and glycine (Gly) to the bovine milk-simulated amino acid mixture on the levels of plasma and liver cholesterol were investigated in rats. The diets containing a high amount of Cys lowered significantly the level of plasma cholesterol as the amount of Cys in diets increased. The serum high density lipoprotein (HDL)-cholesterol level and fecal excretion of acidic steroids were higher in rats fed the Cys diets than in those fed the Arg and Gly diets. No differences, however, was observed in the content of liver cholesterol. Liver triglyceride contents elevated significantly on feeding the Arg and Cys diets. Furthermore, liver phospholipid contents elevated significantly on feeding the Arg diet but lowered on feeding the Cys diet. Therefore, these results indicated that the feeding of a high amount of Cys lowers the plasma cholesterol levels as the result of the enhanced conversion of cholesterol to bile acids.